traditional definitions of life involve self-replication and reaction to stimuli. i think DNA is NOT a necessary condition for life as it is theoretically possible an alternate chemistry could perform the encoding function differently.

A virus cannot replicate without a host. Of course, many organisms are dependant on other organisms to survive. I think that it would be good to try to pin down exactly what we mean by replication and respiration - or any other definitions of life. Being specific helps.

_________________“Once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return.” -Anonymous

Is it is considerated aislated, no because they couln't selfreplicate itself, but if you define the enviroment of virus as a life cell, then yes, because virus can selfreplicate on a cell. So virus are life inside life. Remove the host and you kill the virus.

idiom wrote:

Ideas replicate, are they alive?

Using the same argument, no outside of human, but yes if you restrict ideas to that enviroment then yes.

OF course, a lot of people restrict the meaning of life only to selfcontained matter with this properties and anothers like methabolism, so the only life we know is carbon life on Earth.But another people extend that and they don't have problems naming ideas "life" in this sense.

I think that life can only be defined relative to the life we know. The only way you can define anything is according to what you know. So, be the definition general or specific, it has to be an extension of the life we know of. Otherwise, the definition doesn't have any meaning. Or rather, it has a made-up meaning.

_________________“Once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return.” -Anonymous

I'd like to think of life as an opposing force to decay. Non-living things just are, and wither away over time. Living things keep repairing and recreating themselves. In more physical terms, perhaps we could say that something is alive if it comprises one or more processes that locally decrease entropy?

_________________Say, can you feel the thunder in the air? Just like the moment ’fore it hits – then it’s everywhereWhat is this spell we’re under, do you care? The might to rise above it is now within your sphereMachinae Supremacy – Sid Icarus